WASHINGTON - The White House said Friday that a Russian invasion of Ukraine could come within the week, possibly within the next two days, even before the end of the Winter Olympics, and urged Americans to leave the country now. The message marked a sharp escalation in U.S. warnings about possibly impending military action.

U.S. national security adviser Jake Sullivan said the United States did not have definitive information that an invasion has been ordered by Russian President Vladimir Putin. But, he said all the pieces were in place for a major military operation that could start “rapidly” and possibly before the end of the Games on Jan. 20. Many had believed that Putin would not start any incursion into Ukraine until after the Chinese-hosted Olympics ended.

"We can’t pinpoint the day at this point, and we can’t pinpoint the hour, but that is a very, very distinct possibility,” Sullivan said. ”The strong possibility of action, the distinct possibility of action, in a relatively near term time frame ... is backed up by our view of what’s happening on the ground.”

“We continue to see signs of Russian escalation, including new forces arriving at the Ukrainian border,” he added, ramping up the urgency of earlier U.S. warnings. “As we’ve said before, we are in the window when an invasion could begin at any time should Vladimir Putin decide to order it.”

"The risk is high enough and the threat is now immediate enough that prudence demands that it is the time to leave now,” Sullivan said, repeating a caution given to U.S. citizens in Ukraine earlier by Secretary of State Antony Blinken, who is currently in Australia.

“We are not saying that a decision has been taken by President Putin,” Sullivan said. “What we are saying is that we have a sufficient level of concern based on what we are seeing on the ground, and what our intelligence analysts have picked up, that we are sending this clear message.”

President Joe Biden spoke to a number of European leaders on Friday to underscore the concerns raised by U.S. intelligence about the potential imminence of a Russian invasion. Sullivan said the Western leaders were completely united and would respond harshly to a Russian invasion with devastating economic and trade sanctions.

Britain’s defense secretary, meanwhile, was visiting Moscow in another effort to ease tensions over a possible invasion of Ukraine by Russia.

Russia is holding massive war games in neighboring Belarus and insisting that the highly strained relations is not its fault. Russia says it has no plans to invade but wants the West to keep Ukraine and other former Soviet countries out of NATO.